The present invention relates to a method for forming indicia on golf balls. More specifically, the present invention is directed toward the use of a laser beam to form indicia, such as alphanumeric characters, three-dimensional figures, machine-readable coded markings, and the like, on golf ball covers by ablating surface material from the ball.
Golf ball covers are routinely marked with various surface indicia, such as the manufacturer""s logo and trademark, and the play number, which allows golfers using the same type of golf ball to distinguish one player""s ball from that of another. Additional symbols that may also be applied to golf balls include custom figures for promotional purposes as well as specific marks reflecting manufacturing information. These indicia are generally printed to the painted surface of a golf ball using one of a number methods that have been adapted for use with curved surfaces, including pad, stamping, and transfer-tape printing methods.
In the majority of instances, logos and trademarks are applied to golf balls using pad printing processes and equipment. Pad printing employs an etched image plate (i.e., the clichxc3xa9) having a negative etching of the desired image. The image plate, typically, is made of a tough material such as metal, steel, other alloy or photopolymer, which normally has a uniform thickness except for the area defining the negative etched image. The plate may optionally be coated with one or more protectant layers or materials, to enhance its useful life. Typically, the depth of the etched image is from about 5 microns to about 30 microns or any value therebetween.
During pad printing, ink is applied to the image plate, thus filling the etched image. Excess ink is then scraped off the image plate, leaving behind ink only within the etched image. A printing pad is then momentarily lowered and pressed onto the inked image plate to lift ink from the ink-filed etched image onto the printing pad. The ink so lifted defines the shape of the etched image. The inked pad is then momentarily lowered and pressed onto the golf ball, thereby releasing the ink from the pad, onto the spherical surface of the ball, thereby forming an image corresponding to that of the etched cavity. Ink deposited on a golf ball may be cured by heating or by exposure to ultraviolet radiation, depending on the composition of the ink. One example of a pad-printing method employing a UV-curable ink is provided by U.S. Pat. No. 5,770,325 to Keller et al., which discloses an ink composition comprising a UV-curable resin, a colorizing agent, such as a pigment or dye, and a photoinitiator for initiating polymerization of the UV-curable resin.
Other, less frequently used methods for marking golf balls include tape printing and stamp printing. Tape printing involves the use of a heated element corresponding to the image to be transferred, which is applied with pressure to an inked tape held against the surface to be marked. Similarly, stamp printing methods may involve either pressing an inked stamp directly against the surface to be marked or forcing a stamp against an inked sheet placed between the stamp and the surface of the ball. In both instances, obtaining sharp, well-defined images, without affecting the physical properties of the golf ball, can be difficult.
A serious concern that is common to each of these methods, is the durability of the printed images formed. The cured ink not only must adhere tenaciously to the surface to which it is applied, but it also must be sufficiently flexible and resilient to remain on that surface as the golf ball is compressed and distorted upon being struck by a golf club. Therefore, although it is possible to apply images to the outermost surface of a golf ball using these printing methods, in practice, one or more protective layers of transparent coatings, or xe2x80x9ctopcoats,xe2x80x9d are often applied over such indicia.
Alternative methods for the application of indicia to golf balls have been described, which use lasers to form marks upon the outer surface. For example, U.S. Pat. No. 5,248,878 to Ihara (xe2x80x9cthe ""878 patentxe2x80x9d) discloses laser irradiation of a portion of a golf ball cover under certain conditions resulting in a color change in the surface layer portion which is contacted by the laser. Once a mark is formed by the method of the ""878 patent, an opaque coat of paint cannot be applied to the surface of the ball without covering the previously-developed mark.
Holography may be defined as a method of producing a three-dimensional image of an object by recording, on a photographic plate or film, the interference pattern formed upon exposure of the object by a split laser beam. The three-dimensional holographic image is then observed upon illumination of that recorded interference pattern, which is generally carried upon a reflective surface, with, for example, visible light. U.S. Pat. No. 5,651,741 to Masutani et al. (xe2x80x9cthe ""741 patentxe2x80x9d) provides a method for forming surface indicia on a golf ball employing laser-created holographic images. The ""741 patent discloses, in one embodiment, a hologram formed by recoding, on a suitable recording material, the intensity distribution of interference fringes corresponding to the interference pattern created by superimposing a wave front reflected from or transmitted through an object with a reference wave front. In another embodiment, the ""741 patent discloses the application of a metal film or foil bearing a hologram, to a golf ball surface. However, once a hologram is applied to the surface of the golf ball, that surface cannot be covered with another coat of an opaque paint without obscuring the indicia previously applied.
In an alternative embodiment of the ""741 patent, a hologram recording material is applied to the golf ball surface and the hologram is recorded on that material using a laser beam. In still another embodiment disclosed in the ""741 patent, the hologram is formed on the inner surface of a molding die and transferred to the cover as it is formed in that mold. The ""741 patent also indicates that holographic images may be created by optical interference patterns generated by light reflected from the surface of a golf ball carrying a grid of fine depressions and protrusions of a submicron order which have been formed on the cover surface of a golf ball. Similarly, the ""741 patent also discloses generation of images on the surface of a golf ball, which are produced as optical interference patterns generated upon illumination a region comprising sections having different light transmission properties. These sections may be created within a transparent surface layer by partial laser irradiation in those instances where that irradiation causes a physical change in the exposed, transparent layer, which affects its ability to transmit light.
Although each of the above-identified methods may have a specific application for forming indicia on the surface of a golf ball, none is wholly satisfactory. Marking procedures which print images on golf ball covers require rapidly curable, strongly adherent, and resilient ink compositions to be practical. Similarly, methods, similar to those described above employing lasers for marking golf ball covers either depend upon the discovery of a suitable, empirically-determined set of conditions, which create visually detectable surface discolorations or depend upon the generation of holographic images generated by complex optical interference patterns.
Furthermore, these procedures are not well suited for, nor readily adapted to manufacturing processes employing continuous piece numbering. Accordingly, a long-felt need has existed for a labeling process that would provide a means to distinguish golf balls, using either visible marks or, in preferred embodiments, machine-readable marks, both before and after the application of one or more layers of opaque paint. Such a method, which would provide a unique identifier for each ball that is linked, for example, to the specific manufacturing history of that ball, would be particularly useful in large-scale production processes, where it would have immediate applications for, inter alia, quality control, inventory systems, and sorting operations.
Accordingly, there is a long-felt need for a golf ball marking procedure that will avoid either the inflexibility, or the complexity and expense, inherent in prior art methods for forming indicia on golf ball surfaces. The laser-marking procedures of the present invention provide a solution to these unmet needs.
The present invention is directed toward a method for marking a golf ball having a cover where the mark is formed by directing a laser beam onto a portion of the cover whereby material comprising the cover is ablated. In the present method, the laser used provides radiation having a wavelength which is strongly absorbed by at least one component of the cover so that material is removed from the surface in the absence of significant melting or discoloration of the surrounding surface layer. That is, the image formed by the method of the present invention is not detected as a consequence of such changes in surface appearance, rather indicia are created by the removal of material, leaving a machined or engraved image within the cover layer of the marked golf ball.
In another aspect of the present invention, a golf ball carrying the image formed by laser ablation of surface material is coated with at least one layer of opaque paint, which would obviate images formed using prior art methods, which are provided by surface discolorations and the like.
In a further aspect of the present invention, the laser source, which is used to mark a golf ball having a polyurethane cover, provides laser radiation within the infrared waveband. In a preferred embodiment, the laser radiation has a wavelength within the range of from about 9 microns to about 11 microns, and in a more preferred embodiment, a wavelength of about 10.6 microns. Accordingly, in a preferred configuration of the present golf ball marking procedure, a CO2 laser, which may be a tunable CO2 laser, is employed as the source of laser radiation.
In still another aspect of the present invention, the laser beam is controlled by a computer, which is programmed not only to allow deflection of the laser beam in two and three dimensions as it is applied to the surface of the golf ball cover, but also to control the dwell time of the laser beam at each point on the irradiated surface, thereby controlling the amount of surface material ablated at that point and, consequently, establishing the depth of the mark formed within the cover layer. In a preferred aspect of the present marking procedure, the computer is programmed in such a manner that the laser beam is directed toward the golf ball surface so as to form a detectable image which comprises a plurality of markings having pre-determined length, width and depth.
In other preferred aspects of the present marking method, the image formed in the cover layer of a golf ball may comprise alphanumeric characters, machine-readable coded markings, line codes, logos, and combinations thereof.
In another preferred aspect of the present invention, the golf ball cover comprises polyurethane. In still another preferred aspect of the invention, the polyurethane used in the formation of the cover is a product of the reaction between a polyurethane prepolymer and a curing agent with the polyurethane prepolymer being a product formed by the reaction between a polyol and a diisocyanate. Preferably the prepolymer, in turn, is a product formed by the reaction between 4,4xe2x80x2-diphenylmethane diisocyanate and a polyether type polyol and wherein the curing agent is polytetramethyleneoxide-di-p-aminobenzoate
The present invention also contemplates a golf ball marked by the method disclosed herein.